1. Field of the Invention
This invention relates to improvements in a device for opening and closing a side plate of a loading box on a motor truck under no-load condition.
2. Description of the Prior Art
When a side plate or door of the loading box is pivotally opened or closed, the rotational moment resulting from the gravity of the side plate is varied and accordingly, the force required for the opening or the closing is also varied.
The conventional opening-closing auxiliary fitting has been operable with a torsion spring attached to the hinge of the side plate or with a plate spring acting on the side plate. In any of these, the action has gradually increased as the pivotal movement of the side plate progresses downwardly, so that the equilibrium in the course of the pivotal movement has been insufficient in most part of the course. In addition, a point of equilibrium has been present in the course of the opening movement to prevent the door from being fully opened.